1. Some Key Words and Definitions
Sliding Knot--A knot which allows sliding of the wrappings of the knot along a substantially straight portion of the suture limb to tighten the loop. PA1 Post Limb--The straight portion of the suture limb upon which the second limb wraps around to form a sliding knot. A loosely equivalent term sometimes used in the art of knot tying is the "standing part". PA1 Primary Post Limb--The post limb of the first sliding knot. PA1 Wrapping Limb--The free portion of the suture limb that wraps around the post limb to form a sliding knot. Some loosely equivalent terms sometimes used in the art of knot tying are "working end", "running end" or "free end". PA1 Half-hitch--The half-hitch knot is the simplest of all the sliding knot. It is formed by wrapping the suture limb once around the post limb of the suture (one turn). The half-hitch is commonly named either as "under-over" or "over-under" according to the position of the wrapping limb relative to the post limb during the knot forming process. PA1 Direction of Half-hitches--Refers to whether the half-hitch is formed in the over-under sequence or the under-over sequence. Thus if the first half-hitch is an over-under half hitch and the second half-hitch is an under-over half-hitch, the second half-hitch is said to be in the reversed direction to that of the first half-hitch. PA1 Reversing Half-hitches--Refers to two sequential half-hitches tied in reversed direction either on the same post or on the opposite post. PA1 Compound Sliding Knot--A sliding knot that has more than one turn of the wrapping limb, i.e., any sliding knot other than a half-hitch is a compound sliding knot. PA1 Forward Half Flip--The process whereby a half-hitch is converted to a knot with symmetrical throws by applying equal tension to both suture limbs in opposite directions (see transformation of knot going from FIG. 2 to FIG. 1). PA1 Reverse Half Flip--The process whereby a knot with symmetrical throw is converted to a half hitch by releasing tension on one suture limb and applying tension to the other limb. The limb to which tension is applied becomes the post limb (see transformation of knot going from FIG. 1 to FIG. 2). PA1 Full Flip--The process whereby a half-hitch is converted to another type of half-hitch in which the post limbs are switched. This is accomplished by applying tension on the wrapping limb and releasing the tension on the post limb. Note that an "under-over" half-hitch is converted to an "over-under" half-hitch during a full flip (see transformation of knot going from FIG. 3 to FIG. 4 and vice versa). PA1 Primary Knot--This is the first knot that is tied extracorporeally and then transferred to the surgical site by a knot rundown device (sometimes also referred to as a knot tier or knot tensioner). The primary knot can either be a half-hitch, a compound sliding knot, or a double throw symmetrical knot.
2. Discussion
Tying square knots arthroscopically is difficult. As an alternative, sliding knots and half-hitches are frequently used in arthroscopic surgery.
FIGS. 1-13 illustrate various knot tying configurations common in arthroscopic surgery. More particularly, where a first piece of tissue T1 is to be secured to a second piece of suture T2 using a first suture limb L1 and a second suture limb L2, a sliding knot S (FIG. 5) may be formed on the two suture limbs and run down the post limb (L1 in FIG. 5) so as to cinch closed the loop P and thereby bind the tissues T1 and T2 together. In a sliding knot S, the wrapping limb (L2 in FIG. 5) typically forms a shoulder R at the proximal end of the sliding knot S.
In FIGS. 1-13, FIG. 1 illustrates a symmetrical throw; FIG. 2 illustrates an over-under half-hitch; FIG. 3 illustrates an under-over half-hitch; FIG. 4 is the same as FIG. 2; FIG. 5 illustrates various components of a generic lockable sliding knot; FIG. 6 illustrates an overhand throw non-locking sliding knot; FIG. 7 illustrates a modified Duncan loop non-locking sliding knot; FIG. 8 illustrates a distal locking Roeder knot; FIG. 9 illustrates a proximal locking tautline hitch knot; FIG. 10 illustrates an overhand throw sliding knot with locking half-hitches; FIG. 11 illustrates a modified Duncan loop sliding knot with locking half-hitches; FIG. 12 illustrates a Roeder sliding knot with locking half-hitches; and FIG. 13 illustrates a tautline hitch sliding knot with locking half-hitches.
For secure arthroscopic rotator cuff and Bankart repairs, not only must the knot be securely tied but the loop of the knot has to be tied under the desired tension in order to coapt the tissue edges. The current recommended arthroscopic knot tying technique using an initial sliding knot requires that the sliding knot be locked with reversing half-hitches on alternating posts (see, for example, FIGS. 10-13). However, the tension in the loop of the primary sliding knot may slip inadvertently during post-switching. Current knot tying techniques using prior art knot tiers and methods cannot predictably or reliably tie knots under tension.
More particularly, sliding knots tied extracorporeally can be advanced to a repair site inside the body cavity by simply pulling on the post limb. However, pulling on the post limb will cause undesirable traction on the tissue being repaired. As a result, most surgeons would prefer to advance the sliding knot by pushing the sliding knot forward with a knot tier device when pulling on the post limb. In this way the sliding knot can be advanced without undue tension on the tissue. When the knot abuts against the tissue, the margins of the tissue are drawn together by pulling on the post limb and by pushing against the sliding knot with the tip of a knot tier.
However, when tension in the post limb is released, the sliding knot has a tendency to back off due to the resiliency of the soft tissue, particularly in contracted soft tissue such as is often encountered in rotator cuff repairs.
More particularly, as noted above, in prior art techniques the sliding knot is locked by adding reversing half-hitches on alternating posts (see, for example, FIGS. 10-13). However, one deficiency of these prior art methods is that when tension is released on the primary post limb in order to add the first half-hitch on the opposite post, the primary sliding knot backs off before the first half-hitch is formed to lock the primary sliding knot. In other words, prior art knot tier devices and methods cannot lock sliding knots prior to post switching.
A survey of surgical literature indicates that a variety of different sliding knots are used in arthroscopic and laparoscopic surgery. A detailed examination of the construction of these knots shows that each knot can be classified as either non-lockable sliding knots (see FIGS. 6 and 7) or lockable sliding knots (FIGS. 8 and 9). The lockable knots can be further subdivided into distal locking knots (FIG. 8) and proximal locking knots (FIG. 9). In the distal locking knot, tension on the wrapping limb distorts the distal post portion of the knot (FIG. 8), whereas in the proximal locking knot, tension on the wrapping limb distorts the proximal post portion of the knot (FIG. 9). The resistance to knot slippage is increased by the bend in the distorted post portion of the knot. The preventative measures that can be taken to minimize the sliding knot from backing off relates to the classification of the sliding knot.
Backing off in all sliding knots, irregardless of the classification, can be minimized by simply "cinching" the wrappings around the post. Many of the non-locking sliding knots such as the modified Duncan loop (see, for example, FIG. 7) have several wrappings around the initial post and slippage is prevented by tightening the grip of these wrappings. In the lockable sliding knots, pulling on the wrapping limb distorts the post limb. The bend in the distorted post resists the knot from backing off. The disadvantage of the distal locking knot is the difficulty in locking the knot when tension in the knot loop is high. The advantage of the proximally locking knot is the ease with which the knot can be locked under the desired loop tension.
All non-locking knots can be converted to proximal locking knots by stacking a half-hitch knot proximally.
With the current recommended arthroscopic knot tying technique, even the so-called lockable sliding knots are further locked with reversing half-hitches prior to conclusion of the suturing process.